The present disclosure relates to a vehicle fuel system, and particularly to a filler neck cap adapted to close a fuel tank filler neck. More particularly, the present disclosure relates to a filler neck cap having a vacuum-relief valve.
It is desirable to control pressure in a vehicle fuel tank. Whenever the pressure within the tank reaches a predetermined superatmospheric level, a vent passage is opened automatically to vent pressurized fuel vapor from the tank to limit excess pressure buildup. Whenever pressure within the tank drops to a predetermined subatmospheric level, a vent passage is opened to the atmosphere to equalize pressure in the tank with the atmosphere.